so my brakes started to go to the floor, so i decided to work on it,. changed front pads and front calipers and resurfaced rotors, changed master cylinder and in the rear i changed the wheel cylinders. bleed the whole system and still the same! what can be wrong, i tryed to test the booster its okay. i press the brake, turn on the motor and the pedal goes down a little. so the booter should be alright. anyone have ideas thanks in advance!

 

hmmm, maybe your rubber lines to the calipers are failing.

 

im not losing any fluid..how often to brand new master cylinders fail

 

im saying the rubber may be expanding due to the pressure increase. im not sure how often the master cylinders fail.

 

Kind of sounds like the back brakes need to be changed or adjusted up if they are shoes.
That is where you get a good pedal from, assuming you bled them correctly and don't have any leaks.

 

Sounds like the check valve is faulty.Bad lines for sure. Those lines don't last long and most of the time get VERY bad before anyone finally changes them. No, they never leak. Those check valves just wear out. It's a 3 dollar part lol.

 

Does it go all the way to the floor or just settle a couple of inches?

 

Model year? I can help!

 

I'd put my money on flexible brake hoses at this point

Did you bench bleed the master cyl? what about the rest of the system?

 

I can help you, -it's a 97 or 98. Close enough since they're identical.

 

Where did he go ? CRAPS! Lost again.

 

they are a mogruel to bleed, it took us ages, and i mean several attempts to get my system bled right, there seems to be lots of places for airlocks. mine is a 1997.

 

They can be. I've had more problems bleeding the Grand Marquis (04). That was only because I was attempting to bleed it just about dry, then refill w/fresh. The 98 150 has been a little simpler in the past. Able to use the power seat to assist if nobodies around. Haven't had a problem bleeding the truck that way. But, -it also has braided lines that flow very well.

 

Perhaps the relevancy of this thread can shed some light on a problem I am having myself. I just replaced the front pads and rotors on my truck. I was also planning on changing the flex hoses as well but when I tried to take one off I discovered that I wasn't going to be able to remove it without cutting the hard line feeding it; today being a holiday here I couldn't get any brake line to replace with. I put everything back together including that one flex hose back to the caliper. Bled all four corners, and the pedal was still a bit mushy. You can pump the pedal to get it firm, but as soon as the truck is turned on, the pedal goes all the way to the floor. I can drive the truck fine and the brakes do still work, but the pedal has to be pressed almost to the floor and, when stopped, the pedal will still travel a bit. Would this be a bad master cylinder, bad booster, or both?

 

Here's a few system check procedures fellas:

First, from the Symptom chart, -

Condition = Brake pedal goes down fast.

Cause-------Brake fluid level.-----Fix------ FILL the brake master cylinder reservoir. BLEED the system.

Cause-------Air in system.--------Fix------ BLEED the system.

Cause----Brake master cylinder.---Fix ------CARRY OUT the brake master cylinder component test.

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Condition = The brake pedal eases down slowly

Cause-------Air in system.------Fix------BLEED the system.

Cause--Brake master cylinder.---Fix----CARRY OUT the brake master cylinder component test.
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Also...... -




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Component Checks

The Master Cylinder check

1 Disconnect the brake lines at the brake master cylinder.

2 Plug the outlet ports of the brake master cylinder.

3 Apply the brakes.

If brake pedal height cannot be maintained, the brake master cylinder has an internal leak and must be rebuilt or a new master cylinder installed.

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Compensator Port Check

The purpose of the compensator ports in the brake master cylinder is to supply any additional brake fluid required by the system due to brake pad wear and to allow brake fluid returning from the brake lines to the brake master cylinder to enter the brake master cylinder reservoir.

The returning brake fluid will cause a slight turbulence in the brake master cylinder reservoir. Turbulence seen in the brake master cylinder reservoir upon release of the brake pedal is normal and shows that the compensating ports are not plugged.

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Check Valve

The function of the power brake booster check valve is to allow manifold vacuum to enter the power brake booster and prevent the escape of vacuum in case manifold vacuum is lost during sustained full throttle operation.

To test the function of the power brake booster check valve:

1 Start and run the engine for at least 10 seconds.

2 Operate the brake pedal to check for power assist.

3 Disconnect the vacuum booster hose from the power brake booster. Do not remove the power brake booster check valve from the power brake booster.

There should be enough vacuum retained in the power brake booster for at least one more power-assisted brake operation.

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Brake Booster

1 Check the hydraulic brake system for leaks or insufficient fluid.

2 With the transmission in NEUTRAL, stop the engine and apply the parking brake control. Apply the brake pedal several times to exhaust all vacuum in the system.

3 Apply the brake pedal and hold it in the applied position. Start the engine. If the vacuum system is operating, the brake pedal will tend to move downward under constant foot pressure. If no motion is felt, the power brake booster system is not functioning. Continue the test with the following steps.

4 Remove the vacuum booster hose from check valve connection. Manifold vacuum must be available at the check valve end of the vacuum booster hose with the engine at idle speed and the transmission in NEUTRAL. If the manifold vacuum is available to the power brake booster, connect the vacuum booster hose to the power brake booster check valve and repeat Steps 2 and 3 above.

5 Check and if no downward movement of the brake pedal is felt, install a new power brake booster.

6 Operate the engine a minimum of 10 seconds at fast idle. Stop the engine, and let the vehicle stand for 10 minutes. Then apply the brake pedal with approximately 20 lbs of force. The brake pedal feel should be the same as that noted with the engine operating. If the brake pedal feels hard (no power assist), install a new check valve and retest. If the brake pedal feels spongy, bleed the hydraulic system to remove air.